Realization of a practical video-on-demand (VOD) system which can instantly provide program data in response to a request from a receiver has been desired. A VOD system able to individually respond to requests made at all times, however, requires an extremely large sized data transmission apparatus which performs complex processing.
Accordingly, a near-video-on-demand (NVOD) system which can simplify the configuration of the data transmission apparatus while realizing a function similar to that of a VOD system has been proposed. An NVOD system is a system that transmits program data to a plurality of channels at predetermined time intervals and selects the channel for the programs starting from the next time zone in response to requests made in a certain time zone to provide those programs.
The data transmission apparatus used for such an NVOD system also must process a large amount of AV data (audio data and video data) at a high speed. For example, at first the video data to be supplied is transferred from a large capacity recording apparatus in which a lot of data are recorded to a high speed accessible recording apparatus. Next, the data recorded in that recording apparatus is accessed at a high speed in a fraction of the reproduction time of the video data and data recorded at a plurality of locations predetermined times apart are simultaneously reproduced. Further error correction codes are added to the series of reproduced data which are then converted to a predetermined transmission format and transmitted to the transmission lines.
Accordingly, there is a demand for a data transmission apparatus able to perform this processing by a simpler hardware configuration and a data transmission method able to perform it more efficiently.